For most surgical procedures, it is advantageous for a surgeon to compare intra-operative progress and post-operative results with a pre-operative plan to ensure that surgical objectives are met. In some surgical procedures, particularly those involving orthopedic arthroplasty, relatively small deviations from a pre-operative plan can translate into significant differences in the functionality of the patient's anatomy. For example, in joint replacement surgery on the knee or hip, small changes in the positioning of the prosthetic joint components may result in considerable differences in the patient's posture, gait, and/or range of motion.
In the early years of joint replacement surgery, intra-operative evaluation of the reconstructed joint was highly subjective. The evaluation process typically involved the surgeon manual placing the leg in different poses and repeatedly articulating the joint through varying degrees of flexion and extension of the leg, while testing the range of motion and relative stability of the joint based on “look and feel.” This process for intra-operative evaluation was extremely subjective, and the performance of the reconstructed joint was highly dependent on the experience level of the surgeon. Perhaps not surprisingly, it was difficult for patients and doctors to reliably predict the relative success of the surgery (and the need for subsequent corrective/adjustment surgeries) until well after the initial procedure. Such uncertainty has a negative impact on the ability to predict and control costs associated with surgery, recovery, and rehabilitation.
As orthopedic surgeons and researchers became more familiar with the kinematics and/or kinetics of joint function, techniques for intra-operatively measuring specific joint parameters increased the reliability and repeatability of joint reconstruction surgeries. For example, in knee replacement/reconstruction procedures, surgeons have long sought to ensure that the reconstructed joint is properly “balanced.” A poorly-balanced knee can cause undesired condylar separation at the femorotibial interface, instability during flexion and/or extension, and malalignment and/or malrotation, potentially leading to soft tissue damage, improper/excessive implant wear, and general discomfort for the patient. Knee balancing generally refers to the collection of intra-operative processes used by the surgeon to ensure that the reconstructed knee joint restores proper alignment of the leg, appropriate distribution of weight, and stability across a wide range of motion.
There are two conventional techniques for helping orthopedic surgeons balance a knee: gap balancing and measured resection. The gap balancing technique calls for the surgeon to position the femoral component parallel to the resected surface of tibia while the collateral ligaments are equally tensioned. The goal of the gap balancing technique is to maintain a uniform “gap” between the femoral condyles and tibial articular surface for a prescribed uniform tension applied by the collateral ligaments.
The measured resection technique involves resecting the bone based on anatomical landmarks in order to preserve the position of one or more of the anatomical axes associated with the knee joint. To do so, the surgeon makes precision cuts to the bone based on anatomical landmarks of the femur and tibia. During reconstruction of the joint, the surgeon aims to replace the exact thickness of the resected portions to ensure that the reconstructed anatomy (particularly the anatomical axes of rotation) matches the original anatomy of the joint as closely as possible. The theory behind measured resection is that, because everything that is removed is replaced, the original (and ideal) knee balance is restored. One benefit of this technique is that the femur and tibia can be resected independently of one another, so long as the position of the reconstructed axis is maintained.
Regardless of the specific knee balancing technique used, many surgeons rely on measuring devices for independently analyzing/validating certain joint metrics during the procedure. One of the most useful sets of joint metrics includes data indicating the forces present at the tibiofemoral interface. The magnitude and medial-lateral distribution of such forces, for example, can aid the surgeon is determining proper ligament balance and component placement.
Conventional devices for intra-operatively measuring forces use electrical transducers embedded within a joint prosthesis. When the prosthesis is inserted into the joint, compressive forces between the tibia and femur mechanically deform a structural element of the transducer resulting in corresponding change in an electrical output of the transducer. The change in the electrical output is converted by a processor into a force value, which the surgeon uses to make adjustments necessary to balance the knee.
While such conventional devices may accurately measure instantaneous force values in certain situations, such devices may still be inadequate. For example, conventional femorotibial force sensors may be insufficient for measuring the location of medial and lateral forces relative to the corresponding articular surface of the force sensor. Furthermore, many conventional prosthetic force sensors do not include sufficient isolation between the medial and lateral hemispheres of the sensor. As a result, it is difficult for the surgeon to precisely determine the individual forces applied to the medial and lateral articular surfaces.
Additionally, conventional force sensing devices and systems are insufficient in providing the user with ability to combine kinematic and/or kinetic information in order to track the location and magnitude of the medial and lateral forces with respect to joint angles of flexion/extension, varus/valgus, and internal/external rotation. Further, conventional femorotibial force sensing systems do not provide a convenient platform for real-time intra-operative tracking of the movement of the location of the medial and lateral forces as the joint is articulated across the full range of motion. As such, conventional force sensing systems don't provide sufficient capabilities for allowing the surgeon to monitor medial and lateral forces as a function of joint flexion/extension angle and knee alignment.
The presently disclosed systems and methods for intra-operatively tracking joint performance parameters in orthopedic arthroplastic procedures are directed to overcoming one or more of the problems set forth above and/or other problems in the art.